Themify Builder <= 7.8.1 - Unauthenticated Stored Cross-Site Scripting via 'css[fonts]' Parameter

The Themify Builder plugin for WordPress is vulnerable to Stored Cross-Site Scripting via 'css[fonts]' Parameter in all versions up to, and including, 7.8.1 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The nonce required to reach the vulnerable endpoint is embedded in plain sight within the front-end page markup for all visitors, reducing the access control to a CSRF token rather than an authentication barrier and making the endpoint fully exploitable by unauthenticated attackers.